Asphalt pavement is one of the most useful inventions in human society. It provides a low cost surface layer for roads, highways, and multiple other areas where human activity takes place. Asphalt pavement is a combination of two components, asphalt bitumen and suitably sized road gravel. These two components are blended in specific proportions such that the bitumen coats all of the gravel components and bonds them together once they are compacted onto a base surface.
Asphalt bitumen is produced as the end product in the refining of crude oil after lighter components such as gasoline and diesel have been extracted. Road surfacing has turned out to be the perfect end use for the very large quantities of asphalt bitumen which result from the production of fuels to power vehicles, which ultimately need a surface upon which to travel.
It is well understood by experts in the paving industry and even non-experts who drive vehicles over paved roads, that asphalt pavement has one very common and serious flaw which is that it typically develops many cracks at some point in its life. The cracks typically extend through the pavement thickness to the gravel base or subgrade. After this cracking occurs, much expense is usually incurred by towns, cities, governments and all parties responsible for roads and highways in attempts to render the cracked pavement waterproof with crack sealants applied to the cracks. Crack sealants are typically only applied to the bigger cracks while many smaller less visible cracks remain unsealed and may still allow water penetration. It is well understood by experts in this field that if sufficient rain water penetrates through pavement cracks, it will inevitably enter the subgrade, weaken the subgrade and eventually lead to more cracking and more maintenance costs, including pot-hole repairs.
Typically after a number of years of paying for annual crack sealing and other crack related maintenance the decision may finally be made to install a new layer of pavement. This usually involves milling out and removing only two to three inches of the old pavement surface but leaving the remainder of the slab intact. The new layer of pavement is then installed over the surface of the remaining old pavement. If no crack isolating membrane is used, as is usually the case, the cracks which still remained in the old sub-layer of pavement will eventually propagate upwards through the new surface layer by a process known as crack propagation. Crack propagation is a well-known process in the engineering field and is usually caused by repetitive stresses. Pavement constantly undergoes such repetitive stresses due to intermittent vehicle traffic and day time heating versus night time cooling thermal stresses. Inevitably after a few years of stresses, the new layer of pavement will crack.
To attempt to prevent or delay cracking of pavement, various interlayer or sublayer, crack isolating materials have been developed for embedment beneath a layer of new pavement.
A common form of interlayer or sublayer material is a composite membrane composed of an asphalt bitumen coated membrane, a non-woven polyester or polypropylene reinforcement fabric coated with an elastomeric polymer modified asphaltic coating. This waterproof sheet is designed to add strength and isolate existing cracks or joints in existing pavement and be a moisture barrier beneath a layer of new pavement. Typically this type of material has a self-adhesive surface on one side so that it can be temporarily adhered to existing pavement prior to a new layer of pavement being installed.
Commercial examples of such materials are Petromat and Pavegard, produced in North America. These are commonly referred to in the trade as SAMIs, Stress Absorbing Membrane Interlayers.
This latter type of membrane is intended to perform three functions, in that it strengthens the overlay pavement making it more resistant to cracking, and secondly it acts as a crack isolator to prevent or delay crack propagation, and thirdly it waterproofs the underside of the new pavement layer so that even if it should eventually crack, moisture will not be able to enter the subgrade, since the membrane itself will not crack due to the flexible nature of its elastomeric coating and it's strong fabric reinforcement. This greatly reduces the potential for pavement cracks and resulting pot-hole formation.
Another type of SAMI is comprised of an uncoated non-woven sheet of full road lane width installed onto a newly sprayed hot tack coat of asphalt cement then embedded with rubber tired rollers. This method requires the use of a tanker truck with a spray dispenser plus other large membrane laying equipment and is usually only used on large highway projects rather than city streets.
One common impediment which often dissuades the use of the SAMI materials is that their method of installation is not always convenient to the pavement installers and their equipment, and it can cause delays in the paving process.
By virtue of the SAMI materials having to be installed on road surfaces prior to the paving process, various problems can result. Such problems are that the material, whether it be a grid type or a self-adhesive membrane type, may not bond well to the prepared road bed. If the roadbed is an asphalt pavement surface which has been milled, which is often the case, its surface will have a rough texture not conducive to forming a bond to a self-adhesive membrane placed over it.
Also once a SAMI interlayer or sublayer material is installed over a prepared road which is to be paved, machinery and trucks laden with hot pavement mix must travel over the installed material. In doing so, problems may occur such as damage or dislodging of the material, causing serious delays in the paving process. Any unexpected delay in a paving operation can be very serious since trucks loaded with hot mix pavement material must be emptied before it might cool and solidify.
As one can readily deduce, the above described difficulties related to the installation of SAMI materials can serve as an impediment to their use and therefore often deprive the parties paying for the new pavement of the very substantial benefits of the said materials. Paving contractors often resist the use of SAMI materials because of the delays they may create. Accordingly, there is a desire to provide a better method of installation of stress absorbing membrane interlayers, or SAMIs.